Boffins from the Russian space agency are baffled by the odd behaviour of the Phobos-Grunt probe, which seems to be flying all on its own without the aid of its non-firing engines.

The spacecraft, originally meant for a mission to Martian moon Phobos, has been stuck in an Earth orbit for most of this month after two engine bursts to send it on its way failed to happen.

However, instead of falling a little every time it circles the planet, the probe is rising in its orbit, and Roscosmos isn't sure why.

“Unfortunately, we still don’t have any telemetric information from the spacecraft so we don’t understand what’s going on,” Vitaly Davydov, deputy head of the space agency told state news agency RIA Novosti.

“The most interesting part is that Phobos-Grunt is on an oriented flight course but, according to our data, something unusual is happening with it.”

He theorised that the craft's control system might still be functional even though it never set out for the Red Planet. Another possibility is that Phobos-Grunt is losing fuel, causing its orbit to rise.

However, other Russian space experts have suggested that the probe may in fact be flying. The aerodynamic resistance of the craft's solar panels could be turning them into "wings", pushing the ship up.

Whatever the reason, the rising orbit could extend the time Phobos-Grunt manages to stay in its holding pattern until as late as mid-March.

The window of opportunity to contact the probe and get the engines firing so it could fulfil its mission to Mars and Phobos closed yesterday.

The craft can no longer make the trip to the surface of the Martian moon to collect samples, but if Russian engineers can establish contact with the craft, a feat they have been attempting to no avail since it was lost, they could still use it.

Davydov said Roscosmos was "having a good think" about what to do with the probe.

“If it becomes clear that everything has failed and the insurance issue is settled… we will decide what to do next,” he said.

“We have already said that we are planning to make the Moon our next step. It would be reasonable to focus on the Moon,” he added. ®